Periyar Tiger Reserve lies in the Western Ghats in the Idukki District of the Kerala state in India. The terrain of the Reserve is undulating and the drainage is dendrite. North-eastern boundary of the Reserve is a ridge, which also forms boundary between Kerala and Tamil Nadu states for 90 km.
The Periyar lake with an area of 26 sq. km. is the nucleus of the Tiger Reserve. Due to the diverticular shape, it caters to a much more extensive area of forest than would be possible if it was merely a compact lake. The main prey base of tiger is sambar. The other prey animals of tiger are Indian bison and wild boar. Cattle in fringe area also forms an important prey base.
In the present day Reserve area, a dam was constructed across the Periyar river in 1895 to provide irrigation facilities in Tamil Nadu. The forest around the reservoir, the Peiryar Lake, was declared as reserve forest known as Periyar Lake Reserve in 1899. This area was declared as Nellikkampetty Sanctuary (600 sq. km.) in 1934. The Sanctuary was extended to 777 Sq. Km. in 1950 and renamed as Periyar Wildlife Sanctuary. It was declared as a Tiger Reserve in 1978. The Reserve is contiguous with Ranni extending up to Achancovil. The core area of the Reserve, 350 sq. km. was declared a National Park in 1982.